The reduced glutathione (GSH) - Hydra system is being used as a model to investigate the mechanism by which a membrane receptor is activated. We are currently investigating the ionic factors influencing the response, the molecular conformation of the activator (GSH) at the receptor site, the involvement in cyclic nucleotides, and the preparation of affinity columns. The proposed work will continue unfinished parts of the first phase, but will focus primarily on developing an affinity label and affinity column. Using both procedures we plan to isolate receptor protein and compare its properties with known in vivo physical properties of the receptor.